1. Field of Invention
The invention relates to a developing cartridge which is applied to a laser printer.
2. Description of Related Art
U.S. Pat. No. 6,336,014 discloses a structure in which a developing cartridge accommodating toner is detachably attached to a printer. The developing cartridge includes a developing roller that supplies toner to a photosensitive medium and a supply roller that makes contact with the developing roller to supply toner to the developing roller. A layer thickness-regulating blade, which regulates the thickness of a toner layer formed on the surface of the developing roller makes contact with a circumferential surface of the developing roller. A lower film is disposed at a lower part of the developing roller along an axial direction of the developing roller.
The developing cartridge further includes side seals for preventing toner carried on the developing roller from leaking outside of the developing cartridge. The side seals are disposed at both ends of the developing roller with respect to its axial direction so as to make sliding contact with a circumferential surface of the developing roller at the both ends. The layer thickness-regulating blade prevents leakage of toner from an upper part of the developing roller. The lower film prevents leakage of toner from a lower part of the developing roller.
Inside the developing cartridge, toner is generally likely to build up at both ends of the developing roller more than at its center. When toner is moved to the layer thickness-regulating blade, the pressure that toner applies between the developing roller and the layer thickness-regulating blade becomes higher at both ends than at the center. Consequently, the thickness of toner held at both ends of the developing roller is greater than that at the center.
If the laser printer is used for a long term, toner held at both ends of the developing roller, especially near side seals, is scraped off by the side seals by the rotation of the developing roller and may result in toner leakage.